Hinge assembly for deploying the petals of a sectored mirror of an optical space telescope

ABSTRACT

A system is disclosed for deploying the petals of a sectored mirror assembly of an optical space telescope, wherein the sectored mirror includes a central hub and a plurality of petals disposed about the periphery of the central hub, and each petal has a petal root independently hinged to the central hub. The system includes a first hinge assembly having a root mount secured to a petal root and a hub mount secured the central hub, whereby the first hinge assembly affords the petal associated therewith freedom of rotation about a petal hinge axis. The system further includes a second hinge assembly including a root mount secured to the petal root and a hub mount secured to the central hub, whereby the second hinge assembly affords the petal associated therewith freedom of rotation about the petal hinge axis and freedom to expand and contract thermally, and move rigidly along the petal hinge axis in a frictionless, unconstrained manner. The system also includes a latch assembly including a clevis secured to the petal root at a location spaced from the hinge axis and a pair of laterally opposed latch mechanism operatively associated with the central hub for engaging the clevis upon rotation of the petal about the hinge axis from a stowed position to a deployed position.

CROSS-REFERENCE TO RELATED APPLICATION

The subject application is a divisional application of U.S. patentapplication Ser. No. 10/869,072 filed Jun. 16, 2004, now U.S. Pat. No.6,863,408, which is a divisional application of U.S. patent applicationSer. No. 10/216,225 filed Aug. 9, 2002 now U.S. Pat. No. 6,768,582.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to a system for deploying the petals of asectored mirror of an optical space telescope, and more particularly, toa set of hinges for independently connecting a petal of the sectoredmirror to the central hub of the sectored mirror and to a latchmechanism for securing the hinged petal to the central hub in a deployedposition.

2. Background of the Related Art

The success of the Hubble Space Telescope has spurred the development ofother space-based astronomical observatories, including someincorporating a large diameter primary mirror. A number of designs,including the space-based observatory known as the Next Generation SpaceTelescope (NGST), have centered on a primary optic that is between sixand eight meters in diameter.

Several problems must be overcome to realize a space-based astronomicalobservatory having such a large diameter mirror. For example, designsthat propose a large diameter monolithic mirror would presentsignificant manufacturing difficulties and risks. In addition, the sizeand shape of an observatory having a large diameter mirror would beconstrained by the volume and shape payload or cargo bays available oncurrent launch vehicles.

Designs that propose a deployable large diameter mirror present otherproblems. For example, to achieve a desired surface accuracy and opticalquality, the reflective components (e.g., sectors, segments or petals)of the mirror must be aligned to a very high degree of precision, suchas, within about 10 nanometers. In addition, because the space-basedobservatory would experience broad thermal expansion and contraction ofthe deployable reflective components would need to be accommodated.

It would be beneficial therefore, to provide a deployment system for thereflective components of an optical space telescope that exhibits a highdegree of precision and accommodates thermal changes experienced in anoperational environment.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful system fordeploying the petals of a sectored mirror assembly of an optical spacetelescope. The mirror assembly includes a central hub and a plurality ofpetals disposed about the periphery of the central hub. Each petal has apetal root that is independently hinged to the central hub of the mirrorassembly.

The petal deployment system of the subject invention includes a firsthinge assembly having a root mount secured to a petal root and a hubmount secured the central hub. The first hinge assembly is adapted andconfigured to afford the petal associated therewith freedom of rotationabout a petal hinge axis.

The petal deployment system further includes a second hinge assemblyhaving a root mount secured to the petal root and a hub mount secured tothe central hub. The second hinge assembly is adapted and configured toafford the petal associated therewith freedom of rotation about thepetal hinge axis, as well as freedom to expand and contract thermally,and move rigidly along the petal hinge axis in a frictionless,unconstrained manner.

The petal deployment system further includes a latch assembly includinga clevis secured to the petal root at a location spaced from the hingeaxis and a pair of laterally opposed latches that are operativelyassociated with the central hub for engaging the clevis upon rotation ofthe petal about the hinge axis from a stowed position to a deployedposition.

Preferably, the first hinge assembly includes a first hinge shaftdisposed on the petal hinge axis. The first hinge shaft is secured tothe root mount of the first hinge assembly, and supports a plurality ofaxially spaced apart angular contact bearings. The angular contactbearings are formed from silicon nitride, do not require lubrication andare housed within the hub mount of the first hinge assembly.

Preferably, the second hinge assembly includes a second hinge shaftdisposed on the petal hinge axis. The second hinge shaft is supported bythe root mount of the second hinge assembly, and is disposed within acylindrical bearing cage. The bearing cage is formed from PTFE andretains a plurality of ball bearings. The ball bearings are formed fromsilicon nitride and do not require lubrication. The bearing cage isdisposed between an inner bearing race and an outer bearing race, and ishoused within the hub mount of the second hinge assembly.

Preferably, the latch assembly of the subject invention is adapted andconfigured to afford the petal associated therewith freedom to expandand contract thermally, and move rigidly along a latch axis extendingparallel to the hinge axis in a frictionless, unconstrained manner. Eachlaterally opposed latch of the latch assembly includes a latch shaftmounted for linear movement along the latch axis. The clevis of thelatch assembly defines a reception aperture for receiving the laterallyopposed latch shafts, and an actuator is operatively associated witheach latch for moving the latch shaft thereof into engagement with theclevis.

Each shaft is disposed within a cylindrical bearing cage, and eachbearing cage is formed from PTFE. Each bearing cage retains a pluralityof ball bearings formed from silicon nitride, and is disposed between aninner bearing race and an outer bearing race. Each bearing cage ishoused within a hub mount secured to the central hub, and each hub mountincludes a base portion and a cylindrical housing portion.

These and other unique features of the petal deployment system of thesubject invention will become more readily apparent from the followingdescription of the drawings taken in conjunction with the description ofthe preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the subjectinvention appertains will more readily understand how to construct anduse the petal deployment system of the subject invention, reference maybe had to the drawings wherein:

FIG. 1 is a perspective view of an optical space telescope having aprimary mirror assembly that includes a hexagonal central hub portionand six petals with reflective surfaces independently hinged to thecentral hub portion, with each of the six petals disposed in a deployedposition;

FIG. 2 is a perspective view of the optical space telescope of FIG. 1,wherein three of the petals are hingedly mounted to the central hubportion and stowed in an aft position and three of the petals arehindgely mounted to the central hub portion and stowed in a forwardposition;

FIG. 3 is a side elevational view of a petal mounting section of thecentral hub portion of the optical space mirror of FIGS. 1 and 2, asviewed along the mounting surface of the petal root structure,illustrating in top plan view the double throw latch assembly of thesubject invention which is mounted on the central hub portion, andillustrating in side elevational view the two unique assemblies of thesubject invention which are mounted to the petal root structure and thecentral hub portion;

FIG. 4 is a perspective view of the interface region between the petalroot structure and the central hub portion of the optical space mirrorof FIGS. 1 and 2, illustrating the two hinge assemblies of the subjectinvention, and the clevis associated with the latch assembly, which isshown in phantom lines and mounted to the petal root structure;

FIG. 5 is an exploded perspective view of the one degree-of-the-freedomhinge assembly of the subject invention which includes a root mountsecured to the petal root and a hub mount secured to the central hubportion of the optical space telescope of FIGS. 1 and 2;

FIG. 6 is an exploded perspective view the two degree-of-freedom hingeassembly of the subject invention which includes a root mount secured tothe petal root and a hub mount secured to the central hub portion of theoptical space telescope of FIGS. 1 and 2;

FIG. 7 is an exploded perspective view of a latch mechanism of thedouble throw latch assembly of the subject invention which includes anaxially advanceable latch shaft configured to engage the clevis on thepetal root structure shown in FIG. 4 upon rotation of the petal aboutthe hinge axis from the stowed position of FIG. 2 to the deployedposition of FIG. 1;

FIG. 8 is an inverted side elevational view of the double throw latchassembly of the subject invention in an unlatched position with theopposed latch shafts disengaged from the clevis disposed therebetween;and

FIG. 9 is an enlarged, localized and inverted side elevational view ofthe double throw latch assembly of the subject invention in a latchedposition with the opposed latch shafts in engaged with the clevisdisposed therebetween

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals identifysimilar structural features of the petal deployment system of thesubject invention, there is illustrated in FIG. 1 an optical spacetelescope designated generally by reference numeral 10. Optical spacetelescope 10 includes a primary mirror assembly 12 (shown here in adeployed position), a tower 14 that extends from the center of theprimary mirror assembly 12, and a secondary mirror 16 which is mountedatop the central tower 14. The primary mirror assembly or optic 12consists of a hexagonal central hub portion 18 and six petals 20 a-20 fthat are independently hinged to the central hub portion 18.

As illustrated FIG. 2, three of the petals 20 a, 20 c and 20 e arehingedly mounted for stowage in an aft position and three of the petals20 b, 20 d and 20 f are mounted for stowage in a forward position. Eachpetal 20 a-20 f has a launch latch strut 22 associated therewith thatsecures the petal in a stowed position. Each petal 20 a-20 f has afigure-controlled reflective surface 24 that is formed from fused silicafacesheets and a housing 26 formed from a light-weight carbon compositematerial. The shape of the reflective surface 24 of each petal 20 a-20 fis controlled by a plurality of figure control actuators (not shown)positioned within the petal housing 26.

The radially inward end of each petal housing 26 forms a triangularpetal root structure 30 that supports a pair of hinge assemblies 100,200 which are discussed in greater detail hereinbelow. Each of thepetals 20 a-20 f is operatively connected to the central hub portion 18of primary mirror assembly 12 by two hinge assemblies 100, 200 (see FIG.4). The petal root structure 30 also supports a clevis 50 that formspart of a latch assembly 300 operatively associated with the central hubportion 18 for engaging the clevis 50 upon movement of a petal from thestowed position of FIG. 2 to the deployed position of FIG. 1.

Referring to FIG. 3, each paired set of hinges assemblies 100 and 200define a common hinge line or axis A about which the petal associatedtherewith rotates, and along which thermal expansion and contraction, aswell as rigid movement of the petal structure is accommodated. The latchassembly 300 defines a latch line or axis B that is spaced from andparallel to the hinge axis A. The latch assembly 300 is adapted andconfigured to accommodate thermal expansion and contraction, as well asrigid axial movement of the petal structure along latch axis B.

The One Degree of Freedom Hinge Assembly

Referring to FIGS. 3 through 5, hinge assembly 100 is a one degree offreedom hinge assembly (1DOF) in that it is adapted and configured toafford the petal associated therewith freedom of rotation about thepetal hinge axis. Hinge assembly 100 includes a root mount 110 securedto the mounting surface 32 of the root structure 30 of a petal 20, and ahub mount 120 secured a mounting surface 34 of the central hub portion18 of primary mirror assembly 12.

The root mount 110 is defined by a base 112 and pair of upstandingtrusses 114 a and 114 b. The base 112 is secured to the mountingstructure 32 of the petal root structure 30 by a plurality of fasteners35. The trusses 114 a and 114 b have respective hemi-cylindricalchannels 116 a and 116 b for accommodating an axial hinge shaft 130.Channels 116 a and 116 b are further defined and enclosed bycorresponding channeled root mount caps 118 a and 118 b that are securedto the trusses 114 a and 114 b, respectively, by fasteners 37.

Hinge shaft 130 is secured to the root mount 110 of hinge assembly 100by a pair of axially spaced apart woodruff keys 140 a and 140 b. Moreparticularly, woodruff keys 140 a and 140 b are seated in correspondingslots 115 a and 115 b that are respectively formed in the channels 116 aand 116 b of trusses 114 a and 114 b. The two keys 140 a and 140 b arepositioned to engage complementary slots (not shown) that are formed inhinge shaft 130 to secure the orientation of the shaft 130 with respectto the root mount 110.

Hinge shaft 130 is divided into two sections 130 a, 130 b separated byan annular collar 132. The first shaft portion 130 a of hinge shaft 130extends laterally from hinge assembly 100 and is supported within astabilizing block 160 is fixedly secured to the mounting surface 34 ofhub portion 18, as best seen in FIG. 4. The second shaft portion 130 bsupports four axially spaced apart angular contact bearings 150 a-150 ewhich are axially aligned and retained between the annular collar 132and a retaining collar 128. The angular contact bearings 150 a-150 d arepreferably formed from silicon nitride, and do not require lubrication.Each angular contact bearing 150 a-150 d has relatively movable innerand outer races 152 and 154. The inner race 152 of each bearing istightly fit onto the first shaft portion 130 b of hinge shaft 130.

The hub mount 120 of hinge assembly 100 is defined by a base 122 and apair of upstanding trusses 124 a and 124 b. The base 122 is secured tothe mounting structure 32 of the petal root structure 30 by a pluralityof fasteners 35. The trusses 124 and 124 b transition into a cylindricalhousing 126. The outer race 154 of each of the angular contact bearings150 a-150 d is tightly fit within the cylindrical housing 126 of hubmount 120. The four contact bearings are enclosed within the cylindricalhousing 126 by a retainer ring 125 that is secured to the end of thehousing 126 by plurality of threaded fasteners 137.

In operation, when a petal 20 a-20 f of primary mirror assembly 12 ismoved from the stowed position of FIG. 2 to the deployed position ofFIG. 1, the relatively movable inner and outer races 152 and 154 of eachangular contact bearing 150 a-150 d affords rotational movement of theroot mount 110 relative to the hub mount 120 along the axis of the hingeshaft 130. Hinge assembly 100 constrains all other movement relative tothe hinge axis.

The Two Degree of Freedom Hinge Assembly

Referring to FIGS. 3, 4 and 6, hinge assembly 200 is atwo-degree-of-freedom hinge assembly (2DOF) in that it adapted andconfigured to afford the petal associated therewith freedom of rotationabout the petal hinge axis, as well as freedom to expand and contractthermally, and move rigidly along the petal hinge axis in africtionless, unconstrained manner. Hinge assembly 200 includes a rootmount 210 secured to the mounting surface 32 of the root structure 30 ofa petal 20, and a hub mount 220 secured to the mounting surface 34 thecentral hub portion 18 of the primary mirror assembly 12. The root mount210 is defined by a base 212 and pair of upstanding trusses 214 a and214 b. The base 112 is secured to the mounting structure 32 of the petalroot structure 30 by a plurality of fasteners 35. The trusses 214 a and214 b have respective hemi-cylindrical channels 216 a and 216 b foraccommodating an axial hinge shaft 230. Channels 216 a and 216 b arefurther defined and enclosed by corresponding channeled root mount caps218 a and 218 b that are secured to the trusses 214 a and 214 b,respectively, by fasteners 37.

Hinge shaft 230 is supported by the root mount 210, and moreparticularly is seated within the channels formed by trusses 214 a, 214b and root mount caps 218 a, 218 b. A unique bearing assembly 250, thatenables hinge assembly 200 to provide two degrees of freedom, isoperatively associated with hinge shaft 230. Bearing assembly 250includes a cylindrical bearing cage 240 that is preferably formed fromPTFE, and retains a plurality of ball bearings 245 formed from siliconnitride. The ball bearings 245 are arranged in a splined pattern.Bearing assembly 250 further includes a cylindrical inner bearing race252 and a cylindrical outer bearing race 254. The inner bearing race 252is intimately engaged with hinge shaft 230, retained by the annularshaft collar 232. Similarly, the outer bearing race 254 is intimatelyengaged with hub mount 220.

The hub mount 220 of hinge assembly 100 is defined by a base 222 and apair of upstanding trusses 224 a and 224 b. The base 222 is secured tothe mounting structure 32 of the petal root structure 30 by a pluralityof fasteners 35. The trusses 224 and 224 b transition into a cylindricalhousing 226. The outer cylindrical race 254 of bearing assembly 250 isaccommodated within the cylindrical housing 226 of hub mount 220.

In operation, when a petal 20 of primary mirror assembly 12 is movedfrom the stowed position of FIG. 2 to the deploying position of FIG. 1,the relatively movable inner and outer races 252 and 254 of bearingassembly 250 afford rotational and linear movement of the root mount 210relative to the hub mount 220 along the axis of the hinge shaft 230.Consequently, thermal expansion and contraction of the petal rootstructure will be accommodated, along with rigid movement of the rootstructure along the petal hinge axis A in a frictionless, unconstrainedmanner. Hinge assembly 200 constrains all other movement relative to thehinge axis.

The Double Throw Latch Assembly

Referring now to FIGS. 3, 4 and 7 through 9, latch assembly 300 is adouble throw latch assembly that is extremely stable in that it exhibitshigh stiffness and low hysterisis when subjected to operational loadsexperienced during deployment. Latch assembly 300 is adapted andconfigured to afford the petal associated therewith freedom to expandand contract thermally, and move rigidly along the latch axis B. Morespecifically, latch assembly 300 is designed to constrain fourdegrees-of-freedom and allow unconstrained motion relative to the hingeaxis A in two degrees-of-freedom. That is, the latch assembly 300constrains the petal rotational degree-of-freedom about the hinge axisA, as well as the lateral degree-of-freedom and two rotationaldegrees-of-freedom about the hinge axis A.

The latch assembly 300 includes the clevis 50 secured to the mountingsurface 32 of petal root structure 30 and which defines a receptionaperture 52 (see FIG. 4). Latch assembly 300 further includes a pair oflaterally opposed latches 302 a and 302 b which are operativelyassociated with the mounting surface 34 of the central hub portion 18 ofprimary mirror assembly 12 for engaging the reception aperture 52 of theclevis 50 upon movement of a petal from the stowed position of FIG. 2 tothe deployed position of FIG. 1.

Referring to FIG. 7, the laterally opposed latches 302 a, 302 b areidentical in construction and function. Each latch includes a latchshaft 330 mounted for linear movement along latch axis B. An actuator360 disposed within a housing 362 fastened to the mounting surface 34 ofcentral hub portion 18 is coupled to the end of each latch shaft 330 byway of a linkage assembly 380. The actuator 360 is adapted andconfigured to facilitate axial advancement of the latch shaft 330relative to the reception aperture 52 of clevis 50. Linkage assembly 380includes a fore link 382 fastened to the end of latch shaft 330, aprimary medial link 383 and an aft coupling 384 operatively associatedwith the actuator drive shaft 364. Medial link 383 is associated withaft coupling 384 through a biasing member 394, and to fore link 383through a pivot member 393.

Each latch shaft 330 is operatively associated with a bearing assembly350 that includes a cylindrical bearing cage 340 that is formed fromPTFE and configured to retain a plurality of ball bearings 345 formedfrom silicon nitride. The ball bearings 345 are seated in respectiveapertures and are arranged in a spline pattern. Each bearing cage 340 isdisposed between a cylindrical inner bearing race 352 and a cylindricalouter bearing race 354. The inner bearing race 352 is intimately engagedwith latch shaft 330, retained in part by annular shaft collar 332. Theouter bearing race 354 is supported in a hub mount 320.

Hub mount 320 includes a base 322 having upstanding trusses 324 a and324 b fastened to the mounting surface 34 of the central hub portion 18by a plurality of fasteners 335. The trusses 324 a, 324 b transitioninto a cylindrical housing 326. The outer cylindrical bearing race 354is accommodated within the cylindrical housing 326 of hub mount 320.

The relatively movable inner and outer races 352 and 354 of bearingassembly 350 afford rotational and linear movement of the root mount 310relative to clevis 50 along the axis of the hinge shaft 330 when thepetal is in the deployed and latched position. Consequently, thermalexpansion and contraction of the petal root structure will beaccommodated by the latch assemblies 300, along with rigid movement ofthe root structure along the hinge axis in a frictionless, unconstrainedmanner relative to the latch axis B.

With continuing reference to FIG. 7, a tapered bearing 375 is mounted tothe free end of latch shaft 330 by a support hub 380 and secured by afastener 382. Tapered bearing 375 carries a plurality of cylindricalrollers 385 adapted and configured to engage the reception aperture 52of clevis 50, as discussed in more detail hereinbelow.

When petals 20 a-20 f of mirror assembly 12 are independently rotatedinto the deployed positions shown in FIG. 1, the opposed latches 302 a,302 b of latch assembly 300 slide past the clevis 50 without makingcontact therewith. In the deployed position, the reception aperture 52of the clevis 50 on each petal root 30 is aligned with the latch axis Bdefined by the opposed latch shafts 330 a, 330 b of latches 302 a, 302b, as best seen in FIG. 8. At such a time, the tapered bearings 375 a,375 b on the end of latch shafts 330 a, 330 b are spaced from the clevis50. At the appropriate instance, the respective drive shafts 364 a, 364b of actuators 360 a, 360 b, which are coupled to latch shafts 330 a,330 b respectively, are actuated, preferably simultaneously. This, inturn, causes the tapered bearings 375 a, 375 b to translate axially intoengagement with the reception bore 52 of clevis 50, as best seen in FIG.9.

Upon engagement, the rollers 385 within the tapered bearings 375 a, 375b on the end of each latch shaft 330, 330 b contact a reception boreliner 54 secured within the reception bore 52 of clevis 50. During thisengagement, no latching forces are created in the petal root structure.The distance through which the latch shafts 330 a, 330 b travel toengage the reception bore 52 of the clevis 50 is relatively smallcompared to their overall length. This ensures that the bearing cage 340with which each latch shaft 330 a, 330 b is associated does not becomedisplaced from its housing defined by hub mount 320.

The mating forces exerted by the opposed latches 302 a, 302 b on theclevis 50 are equal and opposite, thus ensuring that a moment will notbe applied to the clevis 50 during engagement. This results in the lowhysterisis and high stiffness exhibited by the latch assembly 300 of thesubject invention. Specifically, the double throw latch assembly 300 ofthe subject invention exhibits axial stiffness on the order of 1,000,000lbs/in. Consequently, when the opposed latches 302 a, 302 b are engaged,as shown in FIG. 9, the clevis 50 will not rotate and re-seat with therollers 385 in the bearing 375 a, 375 b on the end of each latch shaft330 a, 330 b.

Although the subject invention has been described with respect topreferred embodiments, those skilled in the art will readily appreciatethat modifications and changes may be made thereto without departingfrom the spirit or scope of the subject invention as defined by theappended claims. Moreover, while the hinge and latch assembliesdisclosed herein have been described and illustrated with respect to aoptical space telescope such as the NGST, it is envisioned that thesemechanism may be employed in other space based optical systems.

1. A petal deployment hinge assembly for connecting a petal of asectored mirror of an optical space telescope to the central hub of thesectored mirror, the hinge assembly comprising: a) a root mount securedto a root of the petal; b) a hub mount secured to the central hub; c) anaxial hinge shaft supported by the root mount; and d) a cylindricalbearing cage disposed about the hinge shaft and housed within the hubmount for affording rotational and axial movement of the root mountrelative to the hub mount along the axis of the hinge shaft.
 2. A petaldeployment hinge assembly as recited in claim 1, wherein the bearingcage is formed from PTFE.
 3. A petal deployment hinge assembly asrecited in claim 1, wherein the bearing cage retains a plurality of ballbearings.
 4. A petal deployment hinge assembly as recited in claim 3,wherein the ball bearings are formed from silicon nitride.
 5. A petaldeployment hinge assembly as recited in claim 4, wherein the bearingcage is disposed between an inner bearing race and an outer bearingrace.